4 PRINCIPLES OF PALAZONTOLOGY. 
undergone changes of such magnitude as to render it seemingly 
irrational to suppose that they could have been produced by 
any process now in existence. If we add to the above the 
prevalent belief of the time as to the comparative brevity of 
the period which had elapsed since the birth of the globe, we 
can readily understand the general acceptance of some form of 
catastrophism amongst the earlier geologists. 
As regards its general sense and substance, the doctrine of 
catastrophism held that the history of the earth, since first it 
emerged from the primitive chaos, had been one of periods of 
repose, alternating with catastrophes and cataclysms of a more 
or less violent character. The periods of tranquillity were sup- 
posed to have been long and protracted; and during each of 
them it was thought that one of the great geological ‘‘ forma- 
tions” was deposited. In each of these periods, therefore, the 
condition of the earth was supposed to be much the same as it 
is now—sediment was quietly accumulated at the bottom of the 
sea, and animals and plants flourished uninterruptedly in suc- 
cessive generations. Each period of tranquillity, however, was 
believed to have been, sooner or later, put an end to by a 
sudden and awful convulsion of nature, ushering in a brief and 
paroxysmal period, in which the great physical forces were 
unchained and permitted to spring into a portentous activity. 
The forces of subterranean fire, with their concomitant pheno- 
mena of earthquake and volcano, were chiefly relied upon as 
the efficient causes of these periods of spasm and revolution. 
Enormous elevations of portions of the earth’s crust were thus 
believed to be produced, accompanied by corresponding and 
equally gigantic depressions of other portions. In this way 
new ranges of mountains were produced, and previously exist- 
ing ranges levelled with the ground, seas were converted into 
dry land, and continents buried beneath the ocean—catastrophe 
following catastrophe, till the earth was rendered uninhabitable, 
and its races of animals and plants were extinguished, never to 
reappear in the same form. Finally, it was believed that this 
feverish activity ultimately died out, and that the ancient peace 
once more came to reign upon the earth. As the abnormal 
throes and convulsions began to be relieved, the dry land and 
sea once more resumed their relations of stability, the condi- 
tions of life were once more established, and new races of ani- 
mals and plants sprang into existence, to last until the super- 
vention of another fever-fit. 
Such is the past history of the globe, as sketched for us, in 
alternating scenes of fruittul peace and revolutionary destruc- 
tion, by the earlier geologists. As before said, we cannot 
